1. Field of the Invention
The present invention relates generally to a system and method for Digital Rights Management (DRM) of Digital Video Broadcasting (DVB). More particularly, the present invention relates to DRM of DVB technology among the Open Mobile Alliance (OMA) Broadcasting (OMA-BCAST) standards by OMA, i.e., a Rights Object (RO) in accordance with content purchase.
The DVB technology related to the OMA-BCAST standards is classified into Digital Video Broadcasting-Handheld (DVB-H) applied to a portable receiving terminal, Digital Video Broadcasting-Cable (DVB-C) applied to a cable receiving terminal, Digital Video Broadcasting-Satellite (DVB-S) applied to digital video broadcasting by a satellite, Digital Video Broadcasting-Terrestrial (DVB-T) applied to digital video broadcasting by ground waves, etc. The present invention may be applied to all digital video broadcasting by the OMA-BCAST.
2. Description of the Related Art
Conventionally, when providing paid content through Digital Video Broadcasting (DVB), diverse DRM techniques for enabling only users who have purchased content to use the content have been applied. In most cases, such content is encrypted prior to transmission. Broadcasting content is transmitted in the form of an Internet Protocol (IP) packet at the lowest layer, and this IP packet is encrypted by an IP Security (IPSec) method using a Traffic Encryption Key (TEK). If content data encrypted with TEK in the form of a stream is provided to a DVB receiving terminal, TEK lifetime information set in accordance with a user's content purchase request is added to each data of the content encrypted with TEK. If a time according to the TEK lifetime elapses after the content is played, the content is deleted from a storage of the TEK DVB receiving terminal to manage the digital rights. This IPSec method requires a construction for setting TEK lifetime information in TEK data of the content and operating the TEK lifetime with a timer.
According to this method, however, a temporal gap between time points of the conversion of one TEK data and the conversion of the next TEK data, i.e., a crypto period, may occur. This crypto period is generally set to be longer than the TEK lifetime of the TEK data in consideration of a network delay. However, in order to prevent the cutoff of the broadcasting due to such a network delay, the TEK lifetime should be set to be longer than the TEK lifetime to be originally set. For reference, in the OMA-BCAST standard, it is recommended to set the TEK lifetime to be three times the TEK lifetime to be originally set.
Also, a content provider, in order to overcome the cutoff of the broadcasting due to the playback termination of the current TEK data, transmits, in advance, the next TEK data to the digital video broadcast receiving terminal.
As described above, a user can further view the purchased content or even non-purchased content as long as the TEK lifetime is set to have a margin extending even after the expiration of the content use or as long as the TEK data provided in advance. This is called a sneak post view problem. This sneak post view problem becomes more serious in pay-per-view type services. For example, a whole broadcasting program that has not actually been purchased, may be viewed anyway due to the long TEK lifetime.
It is assumed that the TEK data of the content having a long crypto period is received in the DVB receiving terminal. In this case, if the next TEK data is not received when the playback of the TEK data expires, the playback of the content is cut off to prevent successive playback of the stream. Accordingly, the content provider further lengthens the lifetime of the TEK data to prevent the cutoff of the broadcasting, or even transmits the next TEK data. As a result, the user may continue to view the paid stream for as much as the TEK lifetime provided to have a margin, even if the rights object for the user's content expires or until the next TEK data.
As described above, the intention to solve the network delay causes a new problem regarding the sneak post view.